Solid-phase crystallization of amorphous silicon on ZnO:Al for thin-film solar cells

The suitability of ZnO:Al thin films for polycrystalline silicon (poly-Si) thin-film solar cell fabrication was investigated. The electrical and optical properties of 700 -nm-thick ZnO:Al films on glass were analyzed after typical annealing steps occurring during poly-Si film preparation. If the ZnO:Al layer is covered by a 30 nm thin silicon film, the initial sheet resistance of ZnO:Al drops from 4.2 to 2.2 Ω after 22 h annealing at 600 °C and only slightly increases for a 200 s heat treatment at 900 °C. A thin-film solar cell concept consisting of poly-Si films on ZnO:Al coated glass is introduced. First solar cell results will be presented using absorber layers either prepared by solid-phase crystallization (SPC) or by direct deposition at 600 °C.     

Screen-printed thin YSZ films used as electrolytes for solid oxide fuel cells

A thin yttria-stabilized zirconia (8 mol% YSZ) film was successfully fabricated on a NiO-YSZ anode substrate by a screen-printing technique. The scanning electron microscope (SEM) results suggested that the YSZ film thickness was about 31 μm after sintering at 1400 °C for 4 h in air. A 60 wt% La_0.7Sr_0.3MnO₃ + 40 wt% YSZ was screen-printed onto the YSZ film surface as cathode. A single cell was tested from 650 to 850 °C using hydrogen as fuel and ambient air as oxidant, which showed an open circuit voltage (OCV) of 1.02 V and a maximum power density of 1.30 W cm⁻² at 850 °C. The OCV was higher than 1.0 V, which suggested that the YSZ film was quite dense and that the fuel gas leakage through the YSZ film was negligible. Screen-printing can be a promising method for manufacturing YSZ films for solid oxide fuel cells (SOFCs).     

Preparation of Cu2ZnSnS4 thin films by sulfurizing electroplated precursors

Cu₂ZnSnS₄ (CZTS) thin films were prepared by sulfurizing precursors deposited by electroplating. The precursors (Cu/Sn/Zn stacked layers) were deposited by electroplating sequentially onto Mo-coated glass substrates. Aqueous solutions containing copper sulfate for Cu plating, tin sulfate for Sn plating and zinc sulfate for Zn plating were used as the electrolytes. The precursors were sulfurized by annealing with sulfur at temperatures of 300, 400, 500 and 600 °C in an N₂ gas atmosphere. The X-ray diffraction peaks attributable to CZTS were detected in thin films sulfurized at temperatures above 400 °C. A photovoltaic cell using a CZTS thin film produced by sulfurizing an electroplated Sn-rich precursor at 600 °C exhibited an open-circuit voltage of 262 mV, a short-circuit current of 9.85 mA/cm² and an efficiency of 0.98%.     

Effects of step-deposition on structures and properties of transparent conducting aluminum-doped zinc oxide films prepared by DC magnetron sputtering

The 2 wt% aluminum-doped zinc oxide films (AZO) was sputtered on corning glass plate at temperatures of 30–200 °C by DC magnetron sputtering using ceramic target. The microstructures and electrical resistivity of thin films were investigated by scanning electron microscope (SEM) and the van der Pauw method. The optical transmittances of films were measured by UV visible spectrophotometer in the wavelength of 300–900 nm. It was found that the average optical transmittances of specimens were 88%. Highly oriented AZO films in the (0 0 2) direction was observed in specimens as increasing of the substrate temperature. The dense film increased as the temperature increases. In addition, craters of greater depth with more compactness were obtained by step-deposition. The lowest resistivity of 9×10⁻⁴ Ω cm with film thickness of 700 nm was found in specimen grown by step-deposition at 200 °C.     

Electrochemical performance of amorphous-silicon thin films for lithium rechargeable batteries

The effect of deposition temperature and film thickness on the electrochemical performance of amorphous-Si thin films deposited on a copper foil is studied. The electrochemical properties show optimum conditions at 200 °C deposition, and thinner films exhibit superior electrochemical performance than thicker ones. A film of 200 nm Si deposited at 200 °C exhibits excellent cycleability with a specific capacity of ∼3000 mAh g⁻¹. This is probably due to optimization between the strong adhesion by Si/Cu interdiffusion and the film stress.     

Capacity fade of Sony 18650 cells cycled at elevated temperatures: Part I. Cycling performance

The capacity fade of Sony 18650 Li-ion cells increases with increase in temperature. After 800 cycles, the cells cycled at RT and 45 °C showed a capacity fade of 30 and 36%, respectively. The cell cycled at 55 °C showed a capacity loss of about 70% after 490 cycles. The rate capability of the cells continues to decrease with cycling. Impedance measurements showed an overall increase in the cell resistance with cycling and temperature. Impedance studies of the electrode materials showed an increased positive electrode resistance when compared to that of the negative electrode for cells cycled at RT and 45 °C. However, cells cycled at 50 and 55 °C exhibit higher negative electrode resistance. The increased capacity fade for the cells cycled at high temperatures can be explained by taking into account the repeated film formation over the surface of anode, which results in increased rate of lithium loss and also in a drastic increase in the negative electrode resistance with cycling.     

Nanocrystalline tin oxides and nickel oxide film anodes for Li-ion batteries

Tin oxides and nickel oxide thin film anodes have been fabricated for the first time by vacuum thermal evaporation of metallic tin or nickel, and subsequent thermal oxidation in air or oxygen ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements showed that the prepared films are of nanocrystalline structure with the average particle size <100 nm. The electrochemical properties of these film electrodes were examined by galvanostatic cycling measurements and cyclic voltammetry. The composition and electrochemical properties of SnO_x (1<x<2) films strongly depend on the oxidation temperature. The reversible capacities of SnO and SnO₂ films electrodes reached 825 and 760 mAh g⁻¹, respectively, at the current density of 10 μA cm⁻² between 0.10 and 1.30 V. The SnO_x film fabricated at an oxidation temperature of 600 °C exhibited better electrochemical performance than SnO or SnO₂ film electrode. Nanocrystalline NiO thin film prepared at a temperature of 600 °C can deliver a reversible capacity of 680 mAh g⁻¹ at 10 μA cm⁻² in the voltage range 0.01–3.0 V and good cyclability up to 100 cycles.     

Deposition of ZrO2 film by liquid phase deposition

In this study, undoped ZrO₂ thin films were deposited on single-crystal silicon substrates using liquid phase deposition. The undoped films were formed by hydrolysis of zirconium sulfate (Zr(SO₄)₂·4H₂O) in the presence of H₂O. A continuous oxide film was obtained by controlling adequate (NH₄)₂S₂O₈ concentration. The deposited films were characterized by SEM, FT-IR, XRD and DTA. Typically, the films showed excellent adhesion to the substrate with uniform particle diameter about 150 nm. The thicknesses of ZrO₂ film were about 200 nm after 10 h deposition at 30 °C. These films shows single tetragonal phase after heat treated at 600 °C. High annealing temperature (e.g. 750 °C) may result in the phase transformation of (t)-ZrO₂ into (m)-ZrO₂.     

Structural characterization and electrochemical properties of RF-sputtered nanocrystalline Co3O4 thin-film anode

Nanocrystalline Co₃O₄ thin-film anodes were deposited on Pt-coated silicon and 304 stainless steel by radio frequency (RF) magnetron sputtering. The as-deposited and annealed cobalt oxide thin films showed smooth and crack-free morphologies. Both the as-deposited and annealed films exhibited spinel Co₃O₄ phase with nanocrystalline structure. High-temperature annealing enhanced the crystallinity of RF-sputtered cobalt oxide films due to rearrangement of cobalt and oxygen atoms. Electrochemical characterization of RF-sputtered films was carried out by cyclic voltammetry and charge/discharge tests in the voltage range of 0.3–3.0 V. Cyclic voltammetry plots showed that the RF-sputtered Co₃O₄ thin films were electrochemically active. X-ray photoelectron spectrometer (XPS) showed that the fresh cobalt oxide films had two peaks of Co₃O₄. In addition to the binding energy of cobalt oxide, the XPS spectrum of discharged film presented two additional binding energies correspond to Co metal. The first discharge capacities of as-deposited, 300, 500, and 700 °C-annealed films were 722.8, 772.5, 868.4, and 1059.9 μAh cm⁻² μm⁻¹, respectively. High-temperature annealing could enhance the capacity and cycle retention obviously. After 25 cycles discharging, the annealed films showed better cycle retention than as-deposited film. The 700 °C-annealed film exhibited excellent discharge capacity approximated to the theoretical capacity.     

Comparative studies of nickel oxide films on different substrates for electrochemical supercapacitors

Thin nickel oxide (NiO) films were obtained by post-heating of the corresponding precursor films of nickel hydroxide (Ni(OH)₂) cathodically deposited onto different substrates, i.e., nickel foils, and graphite at 25 °C from a bath containing 1.5 mol L⁻¹ Ni(NO₃)₂ and 0.1 mol L⁻¹ NaNO₃ in a solvent of 50% (v/v) ethanol. The surface morphology of the obtained films was observed by scanning electron microscope (SEM). Electrochemical characterization was performed using cyclic voltammetrty (CV), chronopotentiometry (CP) and electrochemical impedance analysis (EIS). When heated at 300 °C for 2 h in air, the specific capacitance of the prepared NiO films on nickel foils and graphite, with a deposition charge of 250 mC cm⁻², were 135, 195 F g⁻¹, respectively. When the deposition charge is less than 280 mC cm⁻², the capacitance of both appears to keep the linear relationship with the deposition charge. The specific capacitance, cyclic stability of the NiO/graphite hybrid electrodes in 1 mol L⁻¹ KOH solution were superior to those on nickel foils mainly due to the favorable adhesion, the good interface behavior between graphite and the NiO films, and the extra pseudo-capacitance of the heated graphite substrates.     

Pt particles supported on conducting polymeric nanocones as electro-catalysts for methanol oxidation

The electrochemical synthesis of conducting nanocones of Pt incorporated poly(3-methyl) thiophene, employing alumina membrane templates and its use as an electrode material for methanol oxidation is reported. The activity (131 mA/cm² at +0.4 V versus Ag/AgCl for a Pt loading of 80 μg/cm²) of nanocone-based electrode was found to be more than one order of magnitude higher compared to the regular poly(3-methyl) thiophene electrode (12.2 mA/cm² at +0.4 V versus Ag/AgCl for a Pt loading of 80 μg/cm²). The chronoamperometric response confirms the better activity and stability of the nanocone-based electrode compared to the commercial 20 wt.% Pt/C (E-TEK) and template-free electrode. The XPS data confirmed the presence of Pt in the metallic state. The nanocone morphology of poly(3-methyl) thiophene, helps in the effective dispersion of Pt particles facilitating the easier access of methanol to the catalytic sites.     

Anode-supported solid oxide fuel cell with yttria-stabilized zirconia/gadolinia-doped ceria bilalyer electrolyte prepared by wet ceramic co-sintering process

To protect the ceria electrolyte from reduction at the anode side, a thin film of yttria-stabilized zirconia (YSZ) is introduced as an electronic blocking layer to anode-supported gadolinia-doped ceria (GDC) electrolyte solid oxide fuel cells (SOFCs). Thin films of YSZ/GDC bilayer electrolyte are deposited onto anode substrates using a simple and cost-effective wet ceramic co-sintering process. A single cell, consisting of a YSZ (∼3 μm)/GDC (∼7 μm) bilayer electrolyte, a La_0.8Sr_0.2Co_0.2Fe_0.8O₃–GDC composite cathode and a Ni–YSZ cermet anode is tested in humidified hydrogen and air. The cell exhibited an open-circuit voltage (OCV) of 1.05 V at 800 °C, compared with 0.59 V for a single cell with a 10-μm GDC film but without a YSZ film. This indicates that the electronic conduction through the GDC electrolyte is successfully blocked by the deposited YSZ film. In spite of the desirable OCVs, the present YSZ/GDC bilayer electrolyte cell achieved a relatively low peak power density of 678 mW cm⁻² at 800 °C. This is attributed to severe mass transport limitations in the thick and low-porosity anode substrate at high current densities.     

Effect of annealing temperature on electrochemical performance of thin-film LiMn2O4 cathode

Spinel LiMn₂O₄ thin-film cathodes were obtained by spin-coating the chitosan-containing precursor solution on a Pt-coated silicon substrate followed by a two-stage heat-treatment procedure. The LiMn₂O₄ film calcined at 700 °C for 1 h showed the highest Li-ion diffusion coefficient, 1.55 × 10⁻¹² cm² s⁻¹ (PSCA measurement) among all calcined films. It is attributed to the larger interstitial space and better crystal perfection of LiMn₂O₄ film calcined at 700 °C for 1 h. Consequently, the 700 °C-calcined LiMn₂O₄ film exhibited the best rate performance in comparison with the ones calcined at other temperatures.     

Large grain Cu(In,Ga)Se2 thin film growth using a Se-radical beam source

Cu(In,Ga)Se₂ (CIGS) thin films were grown by the three-stage process using a rf-plasma cracked Se-radical beam source. CuGaSe₂ (CGS) films grown at a maximum substrate temperature of 550 °C and CuInSe₂ (CIS) and CIGS films grown at the lower temperature of 400 °C exhibited highly dense surfaces and large grain size compared with films grown using a conventional Se-evaporative source. This result is attributed to the modification of the growth kinetics due to the presence of active Se-radical species and enhanced surface migration during growth. The effect on CIGS film properties and solar cell performance has been investigated. Enhancements in the cell efficiencies of 400 °C-grown CIS and CIGS solar cells have been demonstrated using a Se-radical source.     

Electrical characterization of all-solid-state thin film batteries

All-solid-state thin film micro-batteries comprised of a lithium anode, lithium phosphorus oxy-nitride (LiPON) solid electrolyte and Li_xCoO₂ cathode were evaluated at different temperatures from −50 to 80 °C for electrical behavior and impedance raise. The cell dimensions were ∼2 cm long, ∼1.5 cm wide and ∼15 μm thick. The rated capacity of the cells was about 400 μAh. The cells were cycled (charge/discharge) at room temperature over 100 times at a 0.25C rate. The charge and discharge cut-off voltages were 4.2 and 3.0 V, respectively. The cells did not show any capacity decay over 100 cycles. The measured capacity was 400 μAh. The coulombic efficiency was 1, which suggests that the cell reaction is free from any parasitic side reactions and the lithium intercalation and de-intercalation reaction is completely and totally reversible. These cells also have good high-rate performance at room temperature. For example, these cells discharged at a 2.5C rate delivered ∼90% of the capacity at a 0.25C rate. However, the delivered capacities even at a 0.25C rate at 80 and −50 °C were much lower than the room temperature capacity. Cells soaked at −50 °C were not damaged permanently as seen by the near normal behavior when returned to room temperature. However, cells heated to 80 °C were permanently damaged as seen by the lack of normal performance back at room temperature. Cell impedance was measured before and after cycling at different temperatures. The high-frequency resistance (generally ascribed to the electrolyte and other resistances in series with the electrolyte resistance) decreased with decreasing temperature. However, the interfacial resistance increased significantly with decreasing temperature. Further, the electrolyte resistance accounted for ∼2% of the total cell resistance. The cycled cells showed higher impedance than the uncycled cells.     

Cu–Ga–Se thin films prepared by a combination of electrodeposition and evaporation techniques

Cu–Ga–Se thin films were prepared using a combination of electrodeposition and evaporation techniques. A Cu–Se/Mo/glass precursor thin film was first prepared by galvanostatic electrodeposition. On top of this film three different thicknesses of Ga were deposited by evaporation. The Cu–Ga–Se thin films were formed by annealing the Ga/Cu–Se/Mo/glass thin film configuration in a tubular chamber with Se powder, at different temperatures. Thin films were characterized by X-ray diffraction (XRD), photocurrent spectroscopy (PS), inductively coupled plasma (ICP) analysis, and scanning electron microscopy (SEM). The detailed analysis from X-ray reveals that after annealing at 550 °C the CuGaSe₂ phase is formed when the thickness of Ga is 0.25 μm, however at 0.5 μm and 1.0 μm Ga the formation of CuGa₃Se₅ and CuGa₅Se₈ phases is observed respectively. Band gap values were obtained using photocurrent spectroscopy.     

Fabrication and characterization of a YSZ/YDC composite electrolyte by a sol–gel coating method

The compatibility of a composite electrolyte composed of a yttria stabilized zirconia (YSZ) film and a yttria-doped ceria (YDC) substrate in a solid oxide fuel cell (SOFC) that can be operated under 800 °C was evaluated. The YSZ film coated on a YDC substrate was derived from a polymeric YSZ sol using a sol–gel spin coating method followed by heat-treatment at 1400 °C for 2 h. The SEM and XRD analysis indicated that there were no cracks, pinholes, or byproducts. The composite electrolyte comprising a YSZ film of 2 μm thickness and a YDC substrate of 1.6 mm thickness was used in a single cell performance test. A 0.5 V higher value of open circuit voltage (OCV) was found for the composite electrolyte single cell compared with an uncoated YDC single cell between 700 and 1050 °C and confirmed that the YSZ film was an electron blocking layer. The maximum power density of the composite electrolyte single cell at 800 °C, 122 mW/cm² at 285 mA/cm², is comparable with that of a YSZ single cell with the same thickness at 1000 °C, namely 144 mW/cm² at 330 mA/cm². The hypothetical oxygen partial pressure at the interface between the YSZ film and the YDC substrate for the composite electrolyte with the same thickness ratio at 800 °C is 5.58×10⁻¹⁸ atm which is two orders of magnitude higher than the equilibrium oxygen partial pressure of Ce₂O₃/CeO₂, 2.5×10⁻²⁰ atm, at the same temperature.     

Microstructural properties of (In,Ga)2Se3 precursor layers for efficient CIGS thin-film solar cells

(In,Ga)₂Se₃ thin films were deposited on Mo-coated glass substrates by a conventional MBE system. To control the preferred orientation of Cu(In,Ga)Se₂ (CIGS) layers, the deposition temperature dependence T_depo of the (In,Ga)₂Se₃ layer was investigated including observations of both surface morphology and cross-sectional structure, Raman scattering and preferred orientation in the range 50–500 °C. γ-phase (In,Ga)₂Se₃ films exhibited (1 1 0) and (3 0 0) X-ray diffraction lines with a little or no (0 0 6) line contribution for T_depo>300 °C. It was revealed that a (3 0 0) preferred orientation of the (In,Ga)₂Se₃ layer could promote a (2 2 0/2 0 4) orientation of subsequently grown CIGS films, which were obtained only at the moderate temperatures of 300–400 °C during (In,Ga)₂Se₃ deposition.     

Temperature behavior and impedance fundamentals of supercapacitors

Electrochemical impedance spectroscopy (EIS) is one of the most important analytical tools for characterization of electrochemical double-layer capacitors (EDLC). As an example, we have characterized a commercial capacitor (BCAP0350 Maxwell Technologies) by EIS, and we will discuss the typical performance of an EDLC compared to an ideal capacitor.EIS was used to determine internal resistance and capacitance of the same capacitor as a function of temperature and as a function of time during constant voltage tests. In addition, the effect of the electrolyte on the temperature behavior was investigated. While the capacitance is a very weak function of temperature, the ESR increases significantly with reduced temperature. Temperature effects are much more pronounced for propylene carbonate (PC) than for acetonitrile (AN)-based electrolytes. From the data obtained at various temperatures and voltages, we could determine acceleration factors for the degradation. On the basis of an Arrhenius plot of the leakage current measured during load life tests at capacitor voltages between 2.5 V and 3.0 V and temperatures between −40 °C and +70 °C, we determined acceleration factors for capacitor degradation of about 2 for a temperature increase of 10 °C and also a factor of about 2 for a potential increase of 0.1 V.     

Lithium cobalt oxide cathode film prepared by rf sputtering

Thin films of LiCoO₂ prepared by radio frequency magnetron sputtering on Pt-coated silicon are investigated under various deposited parameters such as working pressure, gas flow rate of Ar to O₂, and heat-treatment temperature. The as-deposited film was a nanocrystalline structure with (1 0 4) preferred orientation. After annealing at 500–700 °C, single-phase LiCoO₂ is obtained when the film is originally deposited under an oxygen partial pressure (P_O2) from 5 to 10 mTorr. When the sputtering process is performed outside these P_O2 values, a second phase of Co₃O₄ is formed in addition to the HT-LiCoO₂ phase. The degree of crystallization of the LiCoO₂ films is strongly affected by the annealing temperature; a higher temperature enhances the crystallization of the deposited LiCoO₂ film. The grain sizes of LiCoO₂ films annealed at 500, 600 and 700 °C are about 60, 95, and 125 nm, respectively. Cyclic voltammograms display well-defined redox peaks. LiCoO₂ films deposited by rf sputtering are electrochemically active. The first discharge capacity of thin LiCoO₂ films annealed at 500, 600 and 700 °C is about 41.77, 50.62 and 61.16 μAh/(cm² μm), respectively. The corresponding 50th discharge capacities are 58.1, 72.2 and 74.9% of the first discharge capacity.